1. Field of the Invention
The present invention relates to a collision preventing device or crash pad used for an optical pickup device of an optical disk system for recording or reproducing information to or from an optical information recording medium, such as an optical disk recorded with information on the track, in order to prevent a contact of an objective lens and a surface of the recording medium. More particularly, the invention relates to the objective lens combined with a collision preventing device and a method for manufacturing the same.
2. Description of the Related Art
In recent years, optical information recording media such as optical disks are broadly used as means for recording and reproducing data such as images and sound. In a recording and reproducing apparatus, such information is recorded or reproduced to or from a track of the optical disk by the pickup device relatively moving thereto. To the optical disk system, there is a demand for further increase of density and reduction of size. In the objective lens of the pickup device, the numerical aperture for example is given 0.45 for the CD (Compact Disk) and 0.6 for the DVD (Digital Versatile Disk). Furthermore, the effective diameter of the objective lens has decreased to nearly 3 mm from nearly 4.5 mm in the conventional. As an influence of size reduction for the pickup device, the so-called working distance of between the tip end of the objective lens and the surface of the optical disk has been decreased. As compared with the conventional structure, there is increased possibility of collision of the objective lens with the optical disk surface.
In addition, the thickness of the transmissive substrate has also decreased to 0.6 mm for the DVD from 1.2 mm for the CD. Because the distance is shortened to the recording surface protected by the transmissive substrate, there is increased influence upon the signal based on the injury on the optical disk surface caused by collision of the objective lens.
Meanwhile, recently the advent of the DVD-RW (Digital Versatile -Disk-Rewritable) standard has allowed the user to make record onto the optical disk. During data recording by the user, the presence of injury on the disk surface might cause a serious affection.
Furthermore, in case that an objective lens having a large numerical aperture larger than the conventional one will be employed for the pickup device, there will be decreased the working distance of between the tip end of the objective lens and the surface of the optical disk. As a result, it is necessary to provide a collision preventing device or crash pad having accuracy higher than the conventional in dimension.
In a conventional crash pad, a resin sheet such as Teflon (trade mark) was cut out in a donut shape, and fixed with adhesive tapes to an edge of an actuator bobbin or lens barrel holding the lens. Alternatively, a resin part with a shape that is fitted with the lens barrel was formed to be used as a crash pad fitted with the lens barrel.
In using a crash pad on a two-set objective lens having a high numerical aperture actuated in an extremely short working distance, a sheet-form crash pad has a possibility of coming in contact with the optical disk, because error in the thickness of the adhering layer of the sheet, or floating thereof might occur. In a construction of a molded resin being fitted with an objective lens actuator, there is also a possibility of the crash pad coming in contact with the optical disk, unless accuracy of the molding is kept high, and adhering is done sufficiently,
In either of the cases above-mentioned, the surface of the disk will be damaged unless a material softer than the surface of the disk is used. However, with soft materials, it is difficult to process into a sheet form, or to mold with high precision. It is also difficult to realize a soft crash pad high in precision that conforms to short working distance, for soft cover layers that can realize a low profile cover layer with uniform thickness.
The present invention was made in view of above-mentioned respects, and an object of the present invention is to provide a collision preventing device that can reduce the collision of the effective-diameter area of the objective lens and the surface of the disk, and an objective lens combined with the same and a method for manufacturing the same.
The collision preventing device according to the present invention used for an optical pickup device for recording or reproducing information to or from an optical information recording medium is characterized by having a shock absorbing layer to prevent a contact of an objective lens and a surface of the recording medium. The shock absorbing layer is laminated on the portion extending from the circumferential edge of the effective-diameter area of the objective lens to the outside edge or to the outside of the objective lens and has a thickness in such a manner that said shock absorbing layer comes in contact with the surface of the recording medium prior to said effective-diameter area, when said objective lens comes close to the surface of the recording medium.
In one aspect of the collision preventing device according to the invention, said shock absorbing layer is made of a UV curable resin.
In another aspect of the collision preventing device according to the invention, the pickup device includes a lens barrel, and the lens barrel and said objective lens are adhered by said shock absorbing layer as an adhesive layer.
In a further aspect of the collision preventing device according to the invention, said shock absorbing layer protrudes more toward the recording medium side than an edge face of the lens barrel.
In a still further aspect of the collision preventing device according to the invention, said shock absorbing layer is composed of a laminated body including at least two shock-absorbing-material layers which have hardness numbers different from one another.
A method for manufacturing a collision preventing device used for an optical pickup device for recording or reproducing information to or from an optical information recording medium to prevent a contact of an objective lens and a surface of the recording medium, according to the present invention, is characterized by comprising the steps of:
forming a UV curable resin layer uniformly with a predetermined thickness, fixed to the lens surface of said objective lens; and
exposing the lens surface within an effective-diameter area of the lens surface by removing a part of said UV curable resin layer corresponding to said effective diameter part of the lens surface.
In one aspect of the method for manufacturing a collision preventing device according to the invention, the pickup device includes a lens barrel, and the method further comprising a step of adhering said objective lens and the lens barrel, using said UV curable resin layer as an adhesive layer.
In another aspect of the method for manufacturing a collision preventing device according to the invention, said exposing step includes a step of cutting and peeling off the part of said UV curable resin layer corresponding to said effective diameter part.
In a further aspect of the method for manufacturing a collision preventing device according to the invention, said exposing step includes a step of removing the part of said UV curable resin layer corresponding to said effective diameter part by etching.
In a still further aspect of the method for manufacturing a collision preventing device according to the invention, said exposing step includes a step of pressing and cutting the part of said UV curable resin layer corresponding to said effective diameter part, using a metal mold corresponding to the effective-diameter area.
In another aspect of the method for manufacturing a collision preventing device according to the invention, said forming step of the UV curable resin layer includes a step of repeating to form at least two shock-absorbing-material layers as a laminated body which have hardness numbers different from one another.
An objective lens used for an optical pickup device for recording or reproducing information to or from an optical information recording medium to prevent a contact of an objective lens and a surface of the recording medium, according to the present invention, is characterized by comprising:
an objective lens main body having an effective-diameter area; and
a shock absorbing layer laminated on a portion extending from a circumferential edge of said effective-diameter area to an outside edge or outer side surface of said objective lens and having a thickness in such a manner that, when said objective lens comes close to the surface of the recording medium, said shock absorbing layer comes in contact with the surface of the recording medium prior to said effective-diameter area.
In one aspect of the objective lens according to the invention, said shock absorbing layer is made of a UV curable resin.
In another aspect of the objective lens according to the invention, the pickup device includes a lens barrel, and the lens barrel and said objective lens are adhered by said shock absorbing layer as an adhesive layer.
In a further aspect of the objective lens according to the invention, said shock absorbing layer protrudes more toward the recording medium side than an edge face of the lens barrel
In a still further aspect of the objective lens according to the invention, said shock absorbing layer is composed of a laminated body including at least two shock-absorbing-material layers which have hardness numbers different from one another.